In order to minimize people putting themselves at risk for physical and mental disease, it is important to be able to influence their attitudes and behaviors on health related matters. The proposed work suggests a theoretically based way to influence attitudes and behaviors and culminates in a study designed to influence young people to reduce their risk of contracting skin cancer. The research examines the possibility that people's attitudes can change vicariously from the actions of another person. The proposed research specifically addresses vicarious dissonance. The vicarious dissonance hypothesis holds that a person who observes others behaving in a manner inconsistent with their attitudes has the potential to experience cognitive dissonance vicariously, provided that the actor is a member of the observer's social group. The hypothesis combines dissonance with the theoretical construct of social identity. It is suggested that people who share a common group membership, and who feel strongly identified with their group, tend to take on the characteristics, emotions and motivations of the group's prototypical member. Thus, if a group member acts in such a way that produces dissonance in him or herself, it will also produce dissonance in other group members. Even though the other group members did not act in an attitude discrepant fashion, they will nonetheless experience pressure to change their own attitudes. The research in the proposal is divided into four parts. In Part I, experiments are designed to show that people change their attitudes as a function of the counterattitudinal behavior of other members of their own group and that the attitude change is indeed based on the process of cognitive dissonance. In Part II, experiments directly assess the social identity hypothesis and are designed to study the importance of the prototypicality of the participant, the actor and the attitude issue. Part III experimentally manipulates the strength of group identification and also examines the relative contributions of interpersonal and intragroup identification. Part IV seeks to demonstrate the impact of vicarious dissonance on an important health-related attitude and behavior. The work is directed toward convincing people at risk of skin cancer to use sun block more frequently and effectively.